Electromagnetic control of current flow



Feb. 14, 1961 c. K. LEONARD 2,972,071

ELECTROMAGNETIC CONTROL 0F CURRENT FLOW Filed June 20, 1956 u Y b L AH+! i* I "'N Mmm/wf of /7 mx. 276.! F26- Z mfg-arm' Q /Z 23 IIIIIIIIIHUnited States Patent ELEC'I'ROMAGNETIISSNI'ROL 0F CURRENT Cullman KayeLeonard, Hamilton, Ohio, assigner to the United States of America asrepresented by the Secretary of the Air Force Filed June 20, 1956, Ser.No. 592,697

1 Claim. (Cl. S10-94) This invention relates to the control of the ilowof current in an electrical circuit, and particularly to controllingcurrent flow by sudden changes in the impedance characteristics of sucha circuit.

It is well known that the impedance characteristics of a circuit willvary in accordance with changes in the condition of a magnetic core ofthe saturable reactor type. The present invention utilizes thisprinciple in a novel manner, and provides circuitry adapted for use as ameans of controlling application of energizing power to an electricmotor or equivalent electro-responsive device. Thus the circuitfunctions as a switch, but without requiring physical separation ofswitch contacts.

This type of circuit is lnot subject to the evils of arcing contactswhich have a limited normal life and which often fail in operation dueto welded contacts. The contactor less switch further is not a source ofradio interference as is the conventional contactor type of switch.

In particular applications the methods disclosed in this invention couldbe utilized to result in an improvement over existing equipmentemploying relays having short life `due to contact arcing. The inventionalso lends itself readily to application at reduced pressures whererelay contact arcing is one of the particular problems.

An object of the invention is to provide a new and improved electricalcontrol system.

Another object of the invention is to provide a new and improvedelectrical circuit which operates as a current ilow interrupter withoutthe use of contact surfaces.

A further object of the invention is to provide a method of preventingcontact arcing in control devices and more particularly to preventcontact arcing aggravated by reduced pressure conditions. i

These and other advantages, features and objects of the invention willbecome more apparent from the following description taken in connectionwith the illustrative embodiments in the accompanying drawings wherein:

Fig. l shows the basic sharp cut-off circuit;

Fig. 2 illustrates the sharp cut-oif characteristic of the variableinductance;

Fig. 3 shows an application of the limit switch; and

Fig. 4 shows the limit switch applied in a mechanical take-over system.

The basic series circuit is used as a sharp cut-off circuit triggered bythe increase of inductance of one of the circuit elements. In Fig. l thespecial saturable inductance 12 provides the on-otf action of thecircuit. The special saturable inductance 12 is composed of a singlecoil wound on a core of magnetic material which has a sharp break in itssaturation curve, giving it a distinct knee. This inductance changesimpedance from several hundred ohms to several hundred thousand ohms ingoing from the saturated to the unsaturated condition.

Also with reference to Fig. l, a common mechanically variable inductance13 is used as the actuator in the oiro'uit. The value of capacitance 10is chosen so that a near series resonant circuit condition exists whenthe variable inductance 13 is at some minimum value when the saturableinductance 12 lis saturated. The basic series circuit shown in Fig. 1includes an alternating cun rent supply source 11 and an ammeter 14 as ameans to measure the current ow through the circuit.

Fig. A2 shows the change in current as a function of the mechanicallyvariable inductance 13. As the variable inductance 13 is increased theresonant circuit is detuned slightly and the current decreasesaccordingly. This decrease in current causes an increase in thesatu'rable inductance 12 and it approaches the knee of its saturationcurve. A further minute increase in the variable inductance 13 causesthe saturable inductance 12 to sharply come out of saturation andincrease the series circuit impedance to such a magnitude thatnegligible current ilows. Hence the dow of current has been virtuallyinterrupted.

If this circuit is used in series lwith a control device such as analternating current motor 17 and the mechanized output of the motor isused to change the variable inductance 13, then the circuit becomes alimit switch for the mechanical output of the motor. Fig. 3 illustratesthe circuit wherein the motor 17 is being controlled thereby.Mechanically connected to the motor 17 is a gear box 18 which includes apower take-utf and also another shaft 19 for ldriving a follow-up system20. The core of the variable inductance 13 is adapted to cooperate withthe follow-up system 20 so that the rotation of the motor 17 is, ineffect, controlled and limited by the position'of the core of thevariable inductance 13 as determined by the motor 17 itself.

Fig. 4 shows t-he basic circuit as a switch in a portion of a mechanicaltake-over system from automatic control of some function, such as fuelow of an aircraft gas turbine. A displacement of the manual controllever 23 to the left closes the air gap of the variable inductance 13and causes an increase in inductance. Saturable inductance 12 comes outof saturation, the current goes to near zero and the magnetic clutch l21is deenergized. The rectitier 16 is used as the current source for themagnetic clutch 21 which ordinarily acts to engage and disengage thedrive shaft 22 during automatic operation of the function. If it isdesired to manually control the function, the manual control lever 23may be used with a mechanical take-over linkage 24 connected to thefinal control element 25. Thus, when the control lever 23 is pushedinward to close the air gap the magnetic clutch 21 is deenergized andthe drive shaft 22 stops rotating. The lever 23 may then act through themechanical take-over linkage 24 to regulate the final control element 25in the desired manner.

Although the invention has been described with reference to particularembodiments, it will be understood to those skilled in the art thatvarious changes and modifica tions can be made therein without departingfrom the invention. I intend to be limited only by the true spirit andscope of the appended claim.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent of the United States is:

In an electric system wherein a variable core induct ance operates tocontrol current flow, the combination with said variable core inductanceof a magnetic drive control, means including a saturable core inductancein References Cited in the ie of this patent UNITED STATES PATENTS1,895,357 Warrington Jan. 24, 1933 4 Suits May 12, 1936 Dawson May 27,1952 Spitzer et al Sept. 22, 1953 FOREIGN PATENTS Great Britain Sept. 5,1932 OTHER REFERENCES The Jumping Phenomena in Ferro-Resonance, by 10Yasusi Watanabe; Technology Reports of Tohoku Imperiai University, vol.5, No. 1, 1925; pp. 11-27.

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